The invention relates to a fuel feed circuit for an aeroengine, and more particularly to a circuit that delivers fuel for feeding combustion chamber injectors of the engine and optionally for use as a hydraulic fluid for controlling actuators of variable-geometry members of the engine.
Usually, a fuel feed circuit of an aeroengine has a pump system made up of a low-pressure pump associated with a high-pressure pump. The high-pressure pump is generally in the form of a positive displacement gear pump of constant cylinder capacity that is driven by the engine via an accessory gearbox (AGB). The function of the pump is to deliver fuel at high pressure to the combustion chamber injectors and to the actuators of the variable-geometry members of the engine.
In certain fuel feed circuits, the high-pressure pump is a two-stage pump, i.e. it presents two different stages of gears that are driven simultaneously by the engine and that have different cylinder capacities. With this type of pump, one of the stages is dedicated specifically to feeding the combustion chamber injectors, while the other stage is dedicated to feeding actuators for actuating variable-geometry members of the engine.
Whatever the configuration selected for the high-pressure pump, the rate at which fuel is delivered does not match the real needs of the engine and it exceeds those needs over a wide range of speeds of rotation of the engine. The flow of fuel that is not consumed by the fuel circuit during those speeds of rotation of the engine is therefore returned upstream from the high-pressure pump.
Such forced return of the fuel gives rise firstly to mechanical power being drawn to drive the high-pressure pump, which power does not contribute to the thrust from the engine, and secondly to a rise in the temperature of the fuel. This heating of the fuel has an impact on the overall temperature of the engine since the fuel constitutes the “cold” fluid while the oil constitutes the “hot” fluid. As a result the capacity for cooling by means of the fuel is reduced such that heat needs to be dissipated into the air by means of air/oil heat exchangers, with this being to the detriment of weight, space for installation, and drag.